I have a big bump on my gum near my crown that I had a root canal for.?

Bump. May be an infection. Gargle with salt water but suggest you give your dentist a call. If not available go to an urgent care.
ChronicTooth Abscess. There are a number of common causes for endodontic failure like root fractures, untreated canals, perforations, zips, and transportations, etc. The good news is with the latest advances in technology nonsurgical retreatment is very often possible and highly successful. Proper diagnosis is the key to successful treatment. See your dentist for exam and x-ray.
Bump on gum. This sounds like either a gum abcess or a tooth abcess. It may be the tooth with the crown and root canal, or a neighboring tooth. It is impossible to say for sure without a clinical examination and x-rays. Call your dentist for an examination.
Infection. Most probable cause of symptoms that you describe is infection, either dental infection or gum/bone infection or combination of the two. Please return to your Dentist. Pretreatment of root canal by a specialist Endodontist, removal/treatment/replacement of the crown, or extraction/implant crown may be in order.